1. Field of the Invention
The present invention relates in general to air induction devices used in motor vehicles, and more particularly to air induction devices arranged upstream of an essential unit (viz., unit including a heater and an evaporator) of an automotive air conditioner for directing inside and/or outside air toward the essential unit.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional air induction device of the above-mentioned type will be described with reference to FIG. 3 of the accompanying drawings, which device is disclosed in Japanese Utility Model First Provisional Publication 62-16508.
In the drawing, denoted by numeral 1 is a blower fan which is driven by an electric motor 2. Denoted by numeral 3 is a spirally recessed part of a casing, which part extends around the blower fan 1. The spirally recessed part 3 has an outlet opening 4 which is arranged upstream of an essential unit (not shown, which includes a heater and an evaporator) of an air conditioner installed in a motor vehicle.
The spirally recessed part 3 has upper and lower portions largely opened. Two upper inlet doors 5 are located above the opened upper portion of the spiral part 3, each door 5 being pivotal about a pivot pin 6. When, with the blower fan 1 kept rotated, the doors 5 assume the positions illustrated by the phantom lines, outside air is introduced into the spirally recessed part 3 as indicated by the arrow "A", while, when the doors 5 assume the positions illustrated by the solid lines, inside air is introduced into the spiral part 3 as indicated by the arrows "B" and "B". When the doors 5 assume intermediate positions, both outside air and inside air are introduced to and mixed in the spiral part 3.
It is to be understood that outside air is fresh air outside the vehicle and inside air is air within the vehicle cabin.
Denoted by numeral 7 is a lower case which is secured to the opened lower portion of the spiral part 3. The lower case 7 has a substantially flat lower wall formed with an air induction opening 8. The air induction opening 8 is selectively opened and closed by a lower inlet door 9 which is pivotally connected to the lower case 7 through a pivot shaft 10. When, with the blower fan 1 kept rotated, the lower inlet door 9 assumes the open position as shown, inside air is introduced into the spiral part 3 through the opening 8 as indicated by the arrow "C".
When the air conditioner is under normal operation, the lower inlet door 9 closes the opening 8 and the two upper inlet doors 5 assume the intermediate positions. Thus, under this condition, outside air and inside air are introduced into the spiral part 3 through the opened upper portion of the part 3 and led to the essential unit of the air conditioner by the rotating blower fan 1.
When there is a need of larger amount of air directed to the essential unit, also the lower inlet door 9 is opened.
In the conventional air induction device described hereinabove, the lower inlet door 9 is arranged within the lower case 7, that is, the door 9 is arranged to pivot within the lower case 7, as is understood from the drawing. This arrangement however causes the air induction opening 8 to exhibit a non-negligible resistance against introduction of the inside air into the lower case 7 therethrough even when the lower inlet door 9 assumes its open position. This is because, as is shown by the smaller arrow, part of air led through the opening 8 is forced to collide against the door 9. If the size of the air induction opening 8 is increased for a smoother introduction of the air therethrough, a larger door 9 becomes necessary, which causes a need of increasing force with which the door 9 is handled. Furthermore, increase in size of the door 9 narrows the effective space defined in the lower case 7.